Note: Descriptions are shown in the official language in which they were submitted.
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HOE 87/H 00
AN A~ENr FOR PREVENTING CORROSI~N ON CERAMIC SURFACES
This invention relates to an agent for preventing corro-
sion on surfaces produced from molten s;licates.
These surfaces include, for example, those of enamel,
glazing on porcelain and, in particular, glass.
It ha~ been show~ that silicate surfaces of this type
suffer from corrosion when, above all, they are repeat-
edly brought into con~act with dish~`washing agents and
detergents.
Such dish washing agents and detergents have hitherto
been composed essentially of phosphates~
In attempting to limit the use of phosphates, the
phosphates in these agents have increasingly been
replaced by silicates, in some cases ;n combination
with strong complex;rlg agents.
'
this has the consequence that an increasing amount of
corrosion is observed on glass surfaces when these new
dis~h-washing agents and detergents are lused; this is
even the case when the use of strong comp~exing agents, j
such as, for example, alkylene diphosphon;c acids is
~` omitted.
Surpr;singly, it has now been found that this corrosion
can be substantially avoided using an agent wh;ch con-
tains a fluorine compound which is at least sparingly
soluble in aqueous media. Fluorine compounds of this
type are, for example~ a(kali metal monofluorides, am-
monium monofluorides, alkali meta~ aluminum hexafluor-
ides, ammonium aluminum hexafluorides or tin tetra-
fluoride. However, alkali metal silicofluorides,
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a~moni.um silico~luorides, alkali metal fluoxophosphates and
ammonium fluorophosphates, such as Na2P03F or NaP02F2 or NaPF5,
are particularly suitable for this purpose.
Accordingly, the present invention provides a method for
preventing corrosion on a surface produced ~rom a mol~en silicate
comprising applying to the surface a fluorl.ne compound selected
from the group consisting of alkali metal monofluorides, ammonium
monofluorides, alkali metal aluminium hexafluorides, tin
tetrafluoride, alkali metal fluorophosphates, ammonium
fluorophosphates, alkali metal sllicohexa~luorides and ammonium
silicofluorides.
The present invention also provides a use of a fluorine
compound selected from the group consisting of alkali metal
monofluorides, ammonium monofluorides, alkali metal alumlnium
hexafluoridest tin tetrafluoride, alkali metal fluorophosphates,
: ammonium fluorophosphates, alkali metal silicohexafluorides and
ammonium silicofluorides to prevent corrosion on a surface
produced from a molten silicate.
Preferably, the fluorine compound ls added as a
component of an agent that con~ains 3.1 to 5.0% by weight of the
fluorine compound and, in addition, other components which are
used in dish-washing agents and detergents.
Components of this type are, in general, builders, such
as, for example, alkali metal triphosphates, zeolites, hentonites,
:
:~ polycarboxylatasr phyllosilicates, nitrilotriacetic acid (NTA),
ethylene-diamine-te~raace~ic acid, phosphonocarboxylic acids,
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amido-phosphonic acid etc., alkali carriers such as, for example
Na2SiO3, Na2Si2O5, NaOH and Na2CO3~ surfactants such as, for
example, moderately foaming hlock polymers containing ethylene and
propylene groups, activated chlorine carriers, such as NaOCl, di-
and trichlorisocyanurates, chloramin T, chlorosulfonic acids,
chlorinated orthophosphates etc., fillers such as water, Na2SO4,
SiO2 etc., per~umes and dyes.
In the agents according to the inven~ion, these
components ~ay be present individually or in ~ixtures in additlon
to the fluorine compounds.
The mix~ures produced therefrom advantageously contain
30 to 95% by weight of bullders and alkali carriers together, and
0.1 to 5.0~ by weight, preferably 0.5 to 2.0% by weigh~, of the
fluorine compound, the amount of the latter being selected so that
the content of fluorine in ~he mixtuxe mentioned is a~ least 0.05
by weight.
Since it is generally known that fluorine attacks
surfaces produced from molten silicates - such as, in particulax,
glass - it could not have been predicted by
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those skilled in the art and was entirely surpr;sing
that fl~orine compounds have a corrosion-inhibiting
action on sur-faces of this type, in particular in an
aqueous med;um at a pH greater than 7. I~ the agents
according to the invention are employed, for example,
as dish-washing agents or detergents, a welcome s;de
effect occurs.
It has namely been shown that, when dish-~ashing agents
are used wh;ch are dist~;nguishë"ct'~y a`h;lh content of
s;licates and strong complexing agents, deposits of
varying thickness can be seen on metall;c machine wall
or cutlery surfaces and appear init;a(ly in blue-violet
tarnish colors and later in bluish-whi~e, cloudy, adherent
coatings. It is only possible to remove these coatings
by means of strong ac;ds - such as, for example, concen-
trated hydrochloric acid - with mechanical abrasion.
It has now been shown that the deposits of the type
described and the corrosion on metallic sur~aces can
both be prevented by the agents according to the
invention, in part;cular by those which contain fluoro-
phosphates or silicofluorides as fluorine compound.
References to the corros;on-inh;biting act;on of
certain fluorine compounds in water-carrying pipel;nes
made from metal have already bee~n given ;n US-A-4~613,
45û.
~.
The action of the agents accordiny to the ;nvention is
intended to be descr;bed in greater detail by the
examples which follow.
Example 1 ~Comparison example)
~ standard commercial dishwasher was loaded w;th 12
standard sett;ngs o~ wh;te porcelain as the basic load.
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At the same t;me, 12 each of stainless steel knives,
forks and spoons were added to the load. In addition,
six glasses each of different ~anufacture were placed
in the upper basket. These were the following types of
glass:
a) "ROMA" tumblers, Messrs. Schott-Zwiesel-Glaswerke AG
b) Kolsch glasses, Messrs. YE~A-GLAS
c~ "Alexandra" wine glasses, Messrs. Nachtmann
The glasses had glass materials of different composi-
tions, with unknown analyses, and very di~ferent surfacedesigns due to their ma~ufacturing processes. The d;sh-
washer contents without food residues were washed 1000
times using softened water of Z to a maximum of 5
(German hardness) and using 30 g of detergent per wash-
ing cycle and 3 ml o~ clear r;nsing agent per washingcycle7 The clean1ng cycle was carried out using 6.5 l
of water at 65C. The contents were dried for 30 min-
utes ~ith the door open bet~een each washing cycle.
The detergent used was formulated as follows tInter-
ZO national Electrochemical Commission standard)
50.00 % by weight of sodium tripolyphosphate, partiallyhydrated containing about 7% by weight of water of
crystallization
40.00X by we;ght of sodium metasilicate, anhydrous
2.25% by weight of sodium dichloroisocyanurate.2 H20
tNaDCC)
2.00 % by weight of surfactant and
5~75X by weight of sod;um sulphate, anhydrous
~The surfactant used was a block polymer from Messrs 8ASF
Wyandotte Corp. w1th the trade name ~ lurafac Ra 43).
The damage was determined by visual assessment of the
glasses and metal parts after 50, 125, 250, 375~ 500,
750 and 1000 washing cycles. the amount of damage was
evaluated w;th referenc0 to an evaluation table, ~hose
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grad;ng ;n 0.5 Point steps permits good d;fferent;a-
tion. 0 po;nts ;n this table denote no damage~ whereas
3.5 po;nts denote complete corrosion or destruction.
The mean corros;on data are collated in Table I.
Table I
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~ash,~n~ Glass Cutlery
Cycles Roma Alexandra Kolsch ~eives Spoons Forks
_ _
0,5 0 0 0 0 0
125 0,5 0 0,5 0 0 3
250 1,0 0,5 1,0 0 0 0
375 l,S 1,0 1.0 0 0 0
500 1,5 1,5 1,0 0 0 5,5
750 2,0 1,~ 1~5 0,5 0 0,5
1000 2,5 1,5 2~0 1~0 0 î,S
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Example 2
: 1% by weight ~f Na2P03F (in place of 1~ by ~eight
; of Na2S04) ~as added to the d;sh-washing agent
described in Example 1. The course of damage during the
1000 washing cycles is illustrated in Table II.
Table II
Wash,in~ Glass Cutlery
Cycles ~ama Alexandra Kalsch ~;ves Spoons Forks
. __ __ . T ~
0 0 0 0 ~ 0
125 0 0 0 0 G 0
250 0 0 0 0 0 0
~: 375 0 Q 0 0 0 0
n ~ n o o O
:~~750 0 0 0,5 0,5 0 0
lG00 0,5 D 0,5 0,5 0 0
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Co~pared to Example 1, the corros;on inhibition can be
seen clearly.
Example 3
1X by we;ght of Na2SiF6 was added as formulation
(~), ;n place of 1% of Na2S04~ to a low-phosphate
dish-washing agent of the following composition tA)
15% by weight of sodium tripolyphosphate, partially
hydrated, containing 2X by ~e;ght of water of crystal-
lization
60% by weight of sodium metasilicate, anhydrous
2~ by weight of NaDCC
2% by weight of surfactant and
21% by weight o~ Na2504, anhydrous
The corrosion data for these two formulations are com-
pared in Table lll. Using formulation A, the staihlesssteel hous;ng of the dishwasher and the cutlery had
tarnished in a blue-violet colour after about 50 ~ash-
ing cycles. The coating beca~e cloudy ~hite after 1Z5
washing cycles, and the coating was so considerable
after 750 washing cycles that evaluation of the cutlery
could no longer b~ carried out.
Table IIl
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Washing Glass Cutlery
Cycles ~o~a Alex~ndra Kalsch ~ive~ Spoons Foaks
A B A 8 A ~ A 9 ~ B` A 3
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0 0 0 0 0,5 0 1,G 0 1,0 0 ;,0 0
lZ5 0.5 0 0 0 0,5 0 1, 5 0 1 b5 0 1 ~5 0
2$0 1~5 0 0~5 0 1~0 0 1~S 0 1.5 0 1~5 0
;~ 375 1,5 0 1~0 0 1,5 0 2,0 0 1,5 a 2Ao o
500 Z,0 0 1,0 0 2,0 0 2.5 0 2~5 0 2,5 0
750 2~5 0 2,5 Oi5 2,0 0 n.e.lO n.e. 0 n.e. 01
1000 2,5 0,5 2,5 0,5 2,0 0 n.e 0 n.e. 0 n e 0,5
n.e. = evaluation not possible
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Example 4
2% by we;ght of NaF (D) ~ere added to a for~ulat;on
w;thout triphosphate, but containing hydroxyethylene
d;phosphonic acid (HEDP) as complexing agent (C). The
corrosion data are shown in Table IV.
After about 50 washing cycles using formulation C~
the dishwasher housing and also some oflthe cutlery
handles increasingly exhibited the discoloration and
deposits described in Example 3, but not quite to the
same extent. These phenomena do not appear using for-
mulation D. However, white, rough str;pes which could
not be removed appeared on the dishwasher housing ~rom
about 1Z5 washing cycles.
Formulation composition
C D
2Z~ by weight of HEDP 2X by weight of HEDP
60% by weight of Na2SiO3 60% by weight of Na2SiO3
34% by we;ght of NazC03 32% by weight of Na7C03
Z% by weight of NaDCC 2% by we;ght of NaDCC0 2~ by weight of surfactants 2~ by weight of surfactants
2X by weight of NaF
Table IV
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. ~ash~ng Glass Cutlery
Cycles Ra~a Alexandra Kolsch ~nives Spoons Fnrks
C D C D C 0 C D C D C 0
_ _ .
O O O O O, 5 0 1 ,0 0 1 ,0 0 1 ,0 0
125 0,5 0 O~S 0 0,5 0 2,0 0 1,0 0 1,~ 0
;; 250 1,0 0 0,5 0 1.0 0 1.0 0 1,0 0 1,0 0
375 1,5 0 1,0 0 1,0 0 1,5 0 l,S 0 1,~ ~
500 1,5 0 1,0 0 l,S 0 1,5 0 1,5 0 l,S 0
750 2,0 0 1,5 0 Z~0 0 2.0 0 Z,0 0 1,5 0
1000 2, 5 0, 5 2, 0 ~ 2 ,, 5 0 2 G O O ~ 5 2, 0 0 ;' . O O
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The corros;on result in these two exper;ments after 1000
wash;ng cycles was investigated us;ng a scanning elec-
tron microscope for the example of "ROMA" tumbler~ Even
at a magnification of about 10,000 times, hardly any
damage was visible when fluorine ions were present.
Example 5
As for E~ample 4, but Na2P03F was used in formula-
tion D in place of NaF. The course of damage on the
washed pieces was virtually comparable to that for
formulation D. However, no white str;pes were v;sible on
the metalLic housing of the dishwasher even after 1000
washing cycles.
Example 6
On the one hand, a d;shwashing agent of composition E:
; 15 40% by weight of crystalline alkali ~etal phy~losilicate
25% by weight of sodium carbonate, anhydrous.
28.85X by weight of sodium sulphater anhydrous
1.9% by weight of the methylene-vinyl qster of maleic
anhydride, powder (92% of active substance)
20 2.25~ by weight of sodium dichloroisocyanurate.2H20
2% by weight of surfactant
and on the other hand a dishwashing agent of composition
F which essentially corresponded to that of E but in
which the 2% by weight of sodium carbonate were replaced
by ZZ by weight of Na2P03F, were used.
The results of this comparison are collated in Table V.
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'rable V
_
Washing Glass ¦ Cutlery
Cycles ~o~a Alexandra Kolsch ¦ ~nives Spoons Forks
E F E r E ~ ! E F E ~ E
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5G 0 0 0 3 0 5 13 0 0 5 5 G
125 3 ~ 5 0 0 0 5 0 0 0 5
250 0 0 0 0 0 0 0 0 0 0 0 0
375 0,5 0 0 0 0,5 0 0,5 a 0 0 0,5 0
500 0,5 0 0 0 0,5 0 0.5 0 0 0 0,5 0
750 0,5 0 0,5 3 0,5 0 1,0 0 0 o 0,5 0
1000 1,5 C ~ 0,5 0,5 1,~ ol 0 C 0.5
It is clear that even the only sl;ghtl~ corrosive
formulation E based on a phyllosilicate can still be
positively affected as regards total corros;on by the
simultaneous use of a fluorine compound contain;ng
hydrolyzable fluor;de ;ons.
